1. Technical Field
The present invention relates to a projector which forms an image by using illumination light applied to a liquid crystal light valve from an illumination device, and projects the formed image on a screen.
2. Related Art
A type of projection lens unit incorporated in a projector and having a moving lens barrel movable in the direction of the optical axis shifts the moving lens barrel in a direction away from an image forming optical element by the effect of thermal deformation of bimetal so as to correct the change of the focus position (see JP-A-2008-26864).
Moreover, a type of projection side optical system incorporated in a projector has a heat conductive lens barrel made of highly heat conductive material and disposed at a fixing position of a laminated lens included in plural lenses of the optical system to prevent shift or separation of the laminated lens (see JP-A-2008-58654).
Furthermore, there are a type which includes a cam ring having a temperature coefficient different from that of a correction barrel and cancels the shift of the focus by the movement of the cam ring (see JP-A-2004-264570), and a type which shifts a refraction optical lens in the direction of the optical axis by using a piezoelectric element to control the focus (see JP-A-2002-207168).
According to the projection lens unit disclosed in JP-A-2008-26864, the lens barrel has complicated structure and thus imposes optical design limitations. Particularly, incorporating a bimetal correcting mechanism in the small lens barrel is difficult.
Also, the projection side optical system shown in JP-A-2008-58654 is only a heat conductive lens barrel and thus cannot positively correct the change of the focus position caused by temperature changes.
The technology of JP-A-2004-264570 has complicated structure of the lens barrel, and the technology of JP-A-2002-207168 requires a special control circuit for the piezoelectric element.